1. Field of the Invention
The present invention relates to a heating device which can be used in a fixing device for heating and thereby fixing an unfixed image such as a toner image onto a record member bearing the unfixed image in an electrophotographic image forming apparatus such as a copying machine, printer or the like, and also relates to a heating rotary member which is one component of the heating device.
2. Description of Related Art
A fixing device in an image forming apparatus such as a printer or a copying machine generally includes a heating device provided with a heating roller. A record member bearing an unfixed image such as a toner image is moved between the heating roller and a backup member (generally, a pressure roller) opposed thereto, so that the unfixed image is heated and pressed to be fixed onto the record member.
In many cases, the heating roller includes a heater such as a halogen lamp heater, and the roller is heated by heat radiated from the heater.
However, the heating roller containing the heater such as a halogen lamp heater as a heat source cannot rapidly heat a surface of the heating roller to a predetermined fixing temperature after start of power supply to the heater so that a long preheating time (i.e., a warming-up time) is required before the heating roller reaches the predetermined temperature after power-on of the image forming apparatus. This prevents easy operation of the apparatus.
For reducing the preheating time, a heating roller has been proposed. This roller includes a core roller and a resistance heating member arranged thereon. The resistance heating member is made of a substance, which generates heat when an electric current flows therethrough. The heating roller of this type has a good electrothermal converting efficiency, and can rapidly raise the surface temperature of the heating roller to the predetermined temperature after start of current supply to the resistance heating member so that the preheating time of the heating roller can be reduced.
In the heating device having the heating roller of the above type, for supplying a current to the resistance heating member, the heating device generally has a current receiver member which is electrically connected to the resistance heating member and rotates together with the heating roller, and a current supply member which is in contact with the current receiver member. The resistance heating member is supplied with the current through these supply and receiver members.
More specifically, the proposed heating device has such a structure that a ring-shaped current receiver member is arranged at the outer peripheral surface of a core roller for integral rotation, and the current supply member is in contact with the outer peripheral surface of the current receiver member.
Such a heating device is also proposed that a bearing rotatably carrying a heating roller serves also as a current supply member.
However, current supply structures for the resistance heating members other than the above have not been proposed so that heating rollers and heating devices including the same can be designed with only a restricted degree of design flexibility.
In the heating device including the heating roller of such a type that the current supply member is in contact with the outer peripheral surface of the ring-shaped current receiver member, the receiver and supply members slide on each other at a remarkably high speed so that the current supply member is liable to jump up from the current receiver member, resulting in interruption of contact between the receiver and supply members. The high speed sliding tends to wear the receiver and supply members. Further, the sliding causes a large frictional heat, which significantly raise temperatures of the receiver and supply members and therefore causes deterioration of these members. Accordingly, it is difficult to perform stable supply of the current to the resistance heating member.
The stable supply of the current to the resistance heating member is also difficult in the heating device in which the bearing rotatably carrying the heating roller also serves as the current supply member.